Now showing items 1-20 of 139

    • Numerical investigation of particle size segregation in saturated granular flows using CFD-DEM coupling approach

      Cui, Kahlil F. E.; Zhou, Gordon G. D. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Particle size segregation is a common feature in debris-flow deposits and is assumed to develop in a similar way as in dry granular flows where fluid forces are neglected. Solid-fluid coupling however is a defining feature of debris flows and fluid forces must therefore be accounted for in modelling for the segregation that develops therein. This paper presents a numerical investigation of the mechanisms of segregation under the influence of fluid forces. For this, a segment of a fully submerged bi-disperse steady granular flow is simulated using the CFD-DEM method. The solid-fluid interactions come in the form of buoyancy and fluid drag force. It is found that the presence of the fluid generally retards the rate and quality of segregation primarily by promoting the formation of a plug flow in the stream-wise velocity profile. The plug flow region forms at the free surface where it significantly reduces or zeroes out the shear rates thus inhibiting the main mechanisms of segregation, i.e. kinetic sieving and squeeze expulsion, to take place. It is inferred that the rapid shearing that occurs near the base promotes segregation but is unable to proceed towards the free surface due to the presence of the plug flow region that serves as a barrier. The quality of submerged segregation improves at lower angles where the plug flow region is minimized and the usual parabolic shear profile develops.
    • Erosion by experimental debris flows: particle size effects

      Ghasemi, A.; Kaitna, R.; Fritton, P.; Blankenship, B. T.; Feng, Q.; Densmore, A.; de Hass, T.; Hill, K. M. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The mobilization of surface material by particle-laden flows involves phenomenology that cross multiple scales: particle-scale interactions and mesoscopic stresses have significant implications for landscape evolution and associated hazard mitigation issues. Here, we consider the problem of erosion of bed materials by debris flows – flows of boulders, gravel, sand, fine particles, and fluids – as they entrain soils and rocks from steep hillsides. In this paper we report results from laboratory experiments investigating the effect of changing coarse particle concentration in a dry “debris flow” on the erosion of a bed over which it flows. We find that increasing the fraction of coarse particles in the bed often increases the bed erosion. However, for some systems, the details are noisier and harder to discern. We associate the variable erosion and noisiness in part with the competing dynamics of small scale interactions, such as the coarse grain impacts, and larger scale details, such as those related to angles of repose. We also present preliminary results measuring instantaneous erosion rates and demonstrate that size dependence of the erosion rates can vary considerably from that of the net erosion. We conclude by summarizing some limitations of our experiments and ongoing next steps to address these limitations.
    • How does particle-size segregation affect the fluidity of multi-granular debris flows?

      Hotta, Norifumi; Iwata, Tomoyuki; Suzuki, Takuro (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      It is essential to consider the fluidity of a debris-flow front when calculating its impact. Here, we flume-tested monogranular and bigranular debris flows, and compared the results to those of numerical simulations. We used sand particles with diameters of 0.29 and 0.14 cm at two mixing ratios, of 50% and 50% (5:5), and 30% and 70% (3:7), respectively. Particle segregation was recorded using a high-speed video camera. We evaluated the fronts of debris flows at 0.5-s intervals. We then numerically simulated one- dimensional debris flows under the same conditions, and we used the mean particle diameter when simulating mixed-diameter flows. For monogranular debris flows, the experimental and simulated results were in good agreement in terms of flow depth, front velocity, and flux, but the bigranular debris flows were not well-simulated; the simulated flow depth was less than that found experimentally, and the front velocity and flux were greater. The differences may be attributable to the fact that the dominant shear stress was caused by the concentration of smaller sediment particles in the lower flow layers; such inverse gradations were detected in the debris flow bodies. In this situation, most shear stress is supported by smaller particles in the lower layers; the debris-flow characteristics become similar to those of monogranular flows. Consequently, the calculated front velocities were underestimated; particle segregation at the front of bigranular debris flows did not affect fluidity either initially or over time.
    • Valid debris-flow models must avoid hot starts

      Iverson, Richard M.; George, David L. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Debris-flow experiments and models commonly use “hot-start” initial conditions in which downslope motion begins when a large force imbalance is abruptly imposed. By contrast, initiation of natural debris flows almost invariably results from small perturbations of static force balances that apply to debris masses poised in steep channels or on steep slopes. Models that neglect these static balances may violate physical law. Here we assess how the effects of hot starts are manifested in physical experiments, analytical dam-break models, and numerical models in which frictional resistance is too small to satisfy static force balances in debris-flow source areas. We then outline a numerical modeling framework that avoids use of hot starts. In this framework an initial static force balance is gradually perturbed by increasing pore-fluid pressure that may trigger the onset of debris motion. Subsequent increases in pore-fluid pressure, driven by debris motion, may then reduce the debris frictional strength, leading to high flow mobility.
    • Role of topography on the volume of material eroded by debris flows, The

      Kudo, Tsukasa; Uchida, Taro; Sakurai, Wataru (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Prediction of sediment volume of debris flows is the most important factor for designing debris-flow control structures or estimating debris-flow prone area. It has been considered that debris-flow volume may increase due to erosion at the steep channel. So, clarifying erosion volume (in this study, erosion volume is sediment volume in the channel eroded by debris flow) due to debris flow is a key information to mitigate debris-flow disasters. This study hypothesized that erosion volume might be controlled by topography, because it can be thought that the transport capacity of debris flow increased with the increase of stream bed gradient and contributing area. In Recent field observations by Schürch et al. (2011) supported to this hypothesis and showed a correlation, showing the correlation between flow depth and magnitude of erosion. However, detailed information about spatial pattern of erosion depth due to debris flow is still limited. In this study, spatial pattern measurements of erosion volume due to debris flows for 16 debris flows in Japan. LiDAR data taken before and after the debris flow was used for the comparison. Then, examination of stream bed gradient and drainage area derived from the LiDAR dataset was performed. The study found that erosion volume of debris flow increases as slope of stream bed gradient and drainage area increases. The study proposed methods to predict erosion volume due to debris flow using stream bed gradient and drainage area based on the probabilistic relationship between measured erosion volume and topography. That is, it is considered that the topography derived from LiDAR can be used as one of the indicators used in estimating volume of future debris flow.
    • Numerical investigation of deposition mechanism of submarine debris flow

      Liu, Dingzhu; Cui, Yifei; Choi, Clarence E.; Bazai, Nazir Ahmed; Yu, Zhilin; Lei, Mingyu; Yin, Yanzhou (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Submarine debris flow can damage oil and gas transport pipelines with potentially adverse consequences to the environment and to the industrial activity itself. The deposition process of submarine debris flow, which is related to the flow viscosity, is complex due to the slurry diffusion process that happens during the interaction of water and slurry. In addition, a quantitative characterization of the characterize the flow mechanism as influenced by the material density during the deposition process remains a scientific challenge. To fundamentally understand the mechanisms of solid-fluid interactions in fast-flowing submarine debris flows, a series of three-dimensional (3D) numerical simulations using Computational Fluid Dynamics (CFD) were conducted. The Herschel- Bulkley (HB) model was used to define the submarine slurry’s rheological characterization as calibrate through simple rheological experiment. Results reveal that deposition is a mass diffusion process. Shear stress at the bottom and at the top of the slurry leads to velocity differences in the vertical direction which in turn generates a huge vortex, which contributed to a separation of slurry into two parts: the frontal head, and the tail. The velocity difference in vertical direction is helpful for hydroplaning. For higher slurry viscosity case, the flow profile is longer and thicker with a front head that has a lower averaged densities and sharper head angles. In addition, highly viscous slurries have lower average frontal velocities during the deposition process. The mixture density decreases in two stages: quick decreasing stage and stable decreasing stage. In the first stage, the slurry expands quicker than the second stage. Higher viscosities also lead to larger volume expansions which consequently leads to quicker density decrease.
    • Compressibility of solid phase of debris flow and erosion rate

      Miyamoto, Kuniaki; Itoh, Takahiro; Kisa, Hiroshi (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The change in sediment concentration of debris flow causes erosion and sedimentation of the solid phase of debris flows. Moreover, the changing affects the mobility of the flow. Therefore, knowledge of the mechanism of the changing is important to understand the mechanism of debris flow. The changing can be considered as compressibility of the flow of the solid phase. We developed a constitutive equation set of debris flow by concerning energy dissipation. A part of the energy dissipation is due to inelastic collision of particles. This process must be compressible. Therefore, we reinvestigate the process of the inelastic collisions and the effect to the compressibility. As the result, we lead internal energy to control the compressibility and so-called erosion rate equation. According to the erosion rate equation, it depends on bed gradient and energy loss gradient. A flume test is conducted to evaluate the erosion rate equation. by using a prismatic steep slope channel, which inclination is set at 12 degrees. By comparison of experimental result with the erosion rate equation, it is found that the difference between energy gradient and bed gradient to control the erosion/deposition is not so large. It means that the erosion/deposition might be very much sensitive against the unbalance of the energy gradient and bed gradient.
    • Commonalities between debris flows and flow failures

      Moss, Robb Eric S. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Debris flow and flow failure are terms used to describe large displacement slope failures. The initiation or triggering often differs due to the nature and state of the material, but once triggered these two failure mechanisms both tend to behave like a Bingham plastic exhibiting a yield strength and a strain-rate dependent strength. In this paper the rheology of these failures is examined and compared to field data and lab data to find commonalities. A future goal is to move towards a common definition of the physics and a joint empirical database for improved statistics and predictive models. The authors own field investigations in Chile and lab investigations using shake table experiments will be reviewed along with studies by other researchers.
    • Soil characteristics of long-traveling landslides and a hybrid model to predict travel distance

      Usuki, Nobuhiro; Yoshino, Kousuke; Mizumaya, Takahisa (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      When landslides liquefy and sediment movement takes on characteristics of a debris flow, travel distance increases, expanding the range of potential damage. Clarifying the liquefaction mechanism for such phenomena and predicting travel distance are important for evaluating hard and soft measures for controlling landslide damage. The authors have compiled data on landslide travel distance in Japan, used the travel coefficient (Tr) to classify movement of landslide soil masses, and investigated the relationship between landslide movement and soil characteristics with the goal of clarifying the liquefaction mechanism. These results were used to analyze the soil characteristics of long-traveling landslides. The hybrid model developed by Satofuka (2004) was used as a liquefaction model and sensitivity analysis was conducted for the model parameters. Model validity was evaluated by comparing the simulated and actual sediment flow, deposition, and displacement velocity of a landslide that occurred in Niigata Prefecture in March 2004.
    • Research on the movable solid materials under seepage flow effect in debris flow source area, The

      Yang, Shun; Ou, Guo-qiang; Pan, Hua-li; Xie, Zhong-sheng; Yang, Dong-xu (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Solid materials distributed on the surface of watershed transform to debris flow under seepage flow effect is one of the most common disaster type in the mountainous area, especially in the Longmen Fault regions, China. The high frequency of debris- flow event takes a big menace to local people’s safety of life and properties directly, as well as the reconstruction work. Currently, more theory and experiment researches are concentrated on solid materials instability mechanism, debris-flow initiation, movement process of slope-gully system, but fewer research are focused on the moveable critical condition of solid materials under hydrodynamic condition as seepage flow and surface flow. Thus, based on the mechanical balance, through define the theory of the movable solid materials firstly. Then, take a comparison with traditional terms as loosen solid materials, dynamic reserves and efficient solid materials, it found that solid materials move or not is a mechanical problem rather than traditional definition. Thirdly, on the condition of saturated seepage flow, according to setting up geological model and taking mechanical analysis, it gained dynamical formula and resistance formula respectively, then, give confined parameters, it found a liner distribution of dynamical value and resistance value versus depth when the geology model is homogeneous and the seepage flow saturated in whole layer.
    • Overcoming barriers to progress in seismic monitoring and characterization of debris flows and lahars

      Allstadt, Kate E.; Farin, Maxime; Lockhart, Andrew B.; McBride, Sara K.; Kean, Jason W.; Iverson, Richard M.; Logan, Matthew; Smith, Joel B.; Tsai, Victor C.; George, David (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Debris flows generate seismic signals that contain valuable information about events as they unfold. Though seismic waves have been used for along-channel debris-flow and lahar monitoring systems for decades, it has proven difficult to move beyond detection to more quantitative characterizations of flow parameters and event size. This is for two primary reasons: (1) our limited understanding of how the radiated wavefield relates to debris flow characteristics and dynamics, and (2) difficulties quantifying the effects of heterogeneous shallow earth structure on the observed wavefield. The latter issue, essentially our inability to sufficiently separate seismic path effects from source information, is a barrier to improving our understanding of the first issue. We review the progress that has been made toward establishing the theory, models and methods required to use seismic observations to make quantitative measurements of flows and summarize the practical, social, and scientific barriers to progress. We discuss some specific ongoing efforts to overcome some of these barriers, with a focus on how we are using large-scale seismic experiments at the U.S. Geological Survey debris-flow flume to develop methods for directly measuring path effects and to develop and validate theoretical debris flow seismicity models.
    • Topographic change detection at Chalk Cliffs, Colorado, USA, using airborne lidar and UAS-based Structure-from-Motion photogrammetry

      Barnhart, Katherine R.; Rengers, Francis K.; Ghent, Jessica N.; Tucker, Gregory E.; Coe, Jeffrey A.; Kean, Jason W.; Smith, Joel B.; Staley, Dennis M.; Kleiber, William; Wiens, Ashton M. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The Chalk Cliffs debris-flow site is a small headwater catchment incised into highly fractured and hydrothermally altered quartz monzonite in a semiarid climate. Over half of the extremely steep basin is exposed bedrock. Debris flows occur multiple times per year in response to rainstorm events, typically during the summer monsoon season. The frequency of debris flows, and the uniformity of the underlying rock, make Chalk Cliffs an ideal study catchment for translating mechanistic understanding of natural debris flows to other sites. A 2008 National Center for Airborne Laser Mapping (NCALM) airborne lidar survey provides baseline topography for the site; however, heretofore there has been no systematic effort to collect repeat topography of the entire site. Starting in May 2018, we made repeat surveys of the basin with an unmanned aircraft system (UAS). The UAS-based imagery was processed into (x, y, z) point clouds using Structure-from-Motion (SfM) photogrammetry. We georegistered the point clouds using 12 ground control points placed within and around the study basin. In this study we compare the lidar with one SfM point cloud to assess topographic change over a 10-year time period. The difference map provides observational data relevant to understanding sediment provenance and transport at the Chalk Cliffs. The difference image indicates erosion of colluvial surfaces, with limited deposition in the survey area. Some colluvial hillslopes show spatially uniform erosion while others experienced concentrated erosion of up to 3 m depth over a 10-year period.
    • Forecasting and seismic detection of debris flows in pro-glacial rivers at Mount Rainier National Park, Washington, USA

      Beason, Scott R.; Legg, Nicholas T.; Kenyon, Taylor R.; Jost, Robert P.; Kennard, Paul M. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The glaciated Mount Rainier volcano in Southwestern Washington State (USA) has a rich history of outburst floods and debris flows that have adversely impacted infrastructure at Mount Rainier National Park in the 20th and 21st century. Retreating glaciers leave behind vast amounts of unconsolidated till that is easily mobilized during high precipitation intensity fall storms and during outburst floods during warm summer months. At least 60 debris flows and outburst floods have been documented between 1926 and 2017 at Mount Rainier. Debris-flow activity has led to the closure of campgrounds and visitor destinations, which has limited visitor access to large swaths of the park. After a relative lull in activity between 2006 and 2014, the historically debris-flow-prone South Tahoma Glacier released two separate sequences of debris flows in 2015, possibly signaling a reawakening in activity. The August 13, 2015 debris flow was especially well documented by park visitors, seismographs and, most interestingly, a soundscape monitor which recorded an anomalous decrease in river noise prior to the arrival of the first debris flow. The seismograph near Tahoma Creek accurately recorded the passage of each debris-flow surge. Using the day of and historic antecedent weather conditions on past debris-flow days, we have developed a debris-flow hazard model to help predict those days with a higher relative hazard for debris-flow activity park-wide based on prevailing and forecasted weather conditions. Debris flows are detected in near- real-time using the USGS Real-time Seismic Amplitude Measurement (RSAM) tool. If an event is detected, we can then provide alerts to employees and visitors working and recreating in the areas downstream to evacuate. Our goal is to accurately forecast the hazard of a debris flow up to seven days ahead of time and then use RSAM to detect debris flows within minutes of their genesis.
    • Deciphering sediment dynamics in a debris flow catchment: insights from instrumental monitoring and high-resolution topography

      Coviello, Velio; Theule, Joshua I.; Marchi, Lorenzo; Comiti, Francesco; Crema, Stefano; Cavalli, Marco; Arattano Massimo; Lucía, Ana; Macconi, Pierpaolo (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      In mountainous catchments, the quantification of sediment yield is of paramount relevance for land-use planning and design of sediment control structures. However, deciphering the contribution of the different sediment transport processes (debris flows, debris floods and bedload transport) is often challenging as they are strongly controlled by basin morphometry, hydrological regime, and sediment supply. Therefore, long-term instrumental monitoring through catchment-scale sensor networks can provide precious information, especially if coupled with high-resolution topographical surveys. The Gadria catchment, located in the eastern Italian Alps, offers the possibility to perform a systematic monitoring of sediment transport processes. This catchment typically features several low-magnitude flood episodes and a few debris-flow events per year, from late spring to early fall. Starting from 2011, various instruments mainly devoted to debris-flow detection (geophones, video cameras, flow stage sensors) have been installed along the main channel, just upstream of a retention basin. High-resolution topographical surveys of the retention basin are carried out each year, at the beginning and at the end of the summer season and after debris-flow events. Rainfall is measured in the intermediate part of the catchment and in the headwaters, while PIT-tracing of bedload was performed in the main channel. In this work, we present the reconstruction of the sediment dynamics at the catchment scale during the 2014 and 2015 monitoring seasons. Instrumental monitoring was used to estimate the contribution of the different flow processes, and data from topographical surveys to quantify the transported volumes. Results show that (i) coarse sediment yield is driven by sporadic debris flows while flood events allow the continuous fine-sediment migration along the channel network; (ii) volume estimations may be significantly different – up to 30% lower - if performed through a DEM of Difference (DoD) analysis of the retention basin or by analysing monitoring data; (iii) a multi-parametric monitoring is needed to decipher sediment dynamics at catchment scale.
    • Examining the impact force of debris flow in a check dam from small-flume experiments

      Eu, Song; Im, Sangjun (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Debris flow is one of the most hazardous disasters in mountain regions of Korea. Rainfall-induced debris flows have occurred more frequently during past decades due to climate changes. Especially, its threat on many lives and properties in urban or suburban areas have increased. To control debris-flow disaster, check dams have been constructed in forest watersheds since 1985. Although check dams that recently constructed in Korea are expected to function as debris-flow barriers, impact force has not been considered during design procedure. For effective structure design regarding debris-flow disaster, estimation of debris-flow impact force is necessary. Meanwhile, it is well known that impact force is closely related to the flow characteristics of debris flow. In this study, small flume experiments were conducted to analyze the influence of flow characteristics to impact force of debris flow. Flume slope, total volume, and viscosity of mixture were selected as experiment variables. As a result, faster flow velocity was observed on steeper channel slope and larger mixture volume condition. In terms of viscosity, sediment-water mixture flowed faster as the viscosity becomes lower. The effect of flume slope on flow velocity was different as the viscosity of mixtures. However, flowing depth was correlated only to total mixture volume. Impact force was positively correlated to flow velocity and flow depth. By comparing various impact force estimation model, the hydrodynamic model has been selected for the best method to appropriately calculate the design impact force for check dams in small forested watersheds.
    • Vibrational characteristics of debris flow in Taiwan, The

      Huang, Yi-Min; Fang, Yao-Min; Yin, Hsiao-Yuan (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Debris flows have become a common disaster in Taiwan in recent years since the impacts of extreme weathers has been aggravated. To protect people from the debris-flow disasters, a monitoring and warning system was developed by Soil and Water Conservation Bureau (SWCB) in Taiwan. The rainfall-based criteria are used in Taiwan for debris flow warning. Different to rainfall measurement, the ground surface vibrational signal from a debris flow has been studied more widely in recent years. Sensors of geophone (short period seismograph) and broadband seismograph are commonly used for debris flow monitoring. In this paper, the signal analysis of debris flows was performed by calculating the vibrational energy. The comparison of the analysis results indicated that when the energy ratios of at least two of the axes are greater than 1.12, a debris flow is highly likely to occur. The starting point in the increasing trend of vibrational energy implied the possible warning time point for debris flow. Vibration examples of debris flow and earthquakes were also compared in this paper.
    • Monitoring and modeling of debris-flow surges at the Lattenbach creek, Austria

      Huebl, Johannes; Arai, Muniyuki; Kaitna, Roland (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Debris-flow events are often comprised by a sequence of surges, sometimes termed roll waves. The reason for this surging behavior is still a matter of debate. Explanations include the growth of hydraulic instabilities, periodic sediment deposition and release, or grain size sorting. Also, the shape and the velocity of single surges and the implications for hazard mitigation are hard to predict. Here we present results of several years of monitoring debris-flow events at the Lattenbach creek (AUT). The monitoring system includes radar sensors for measuring flow depth at different locations along the channel, as well as a 2-D rotational laser sensor installed over a fixed cross-section that yields a 3-D surface model of the passing debris-flow event. We find that the debris flows at Lattenbach creek exhibited surges for each observed event. The celerity of the surges were up to twice as high as the front velocity. Often, the first surges had highest flow depth and discharge, and showed an irregular geometry. Video recordings reveal that this might be connected to the presence of large boulders and woody debris. On the contrary, the shape of the surges in the second half of the flow, which carried smaller grain sizes and less woody debris, were rather regular and showed a striking geometric similarity, but still high velocities. We tested a recently derived wave equation based on hydraulic theory and found that the shape of these regular roll waves can be reasonably reproduced by that model. The results of our monitoring efforts aim to improve our understanding of the surging behavior of debris flows and provide data for model testing for the scientific community.
    • Monitoring of rainfall and soil moisture at the Rebaixader catchment (Central Pyrenees)

      Hürlimann, Marcel; Oorthuis, Raül; Abancó, Clàudia; Carleo, Luigi; Moya, José (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The instrumental monitoring of torrential catchments is a fundamental research task and provides necessary information to improve our understanding on the mechanisms of debris flows. While most monitoring sites include meteorological sensors and analyze the critical rainfall conditions, only very few contain soil moisture measurements. In our monitoring site, the Rebaixader catchment, 11 debris flows and 24 debris floods were detected during the last nine years. Herein, the initiation mechanisms of these torrential flows were analyzed focusing on the critical rainfall conditions and the soil water dynamics. Comparing the temporal distribution of both rainfall episodes and torrential flows, the Kernel density plots showed maximum values for rainfalls at the beginning of June, while the peak for torrential flows is at July 20th. This means that highest probability of debris flows and debris floods triggering is about 1.5 months later than the one of rainstorms in the catchment. Thus, the antecedent rainfall and especially the soil moisture conditions may influence the triggering of torrential flows. In a second step, a new updated rainfall threshold was proposed including total rainfall duration and mean intensity. The analysis of soil moisture data was more complicated and no clear trends were observed in the dataset. Therefore, additional data has to be recorded in order to quantitatively analyze the role of soil moisture on the triggering of flows and for the definition of thresholds. Some preliminary results show that the soil moisture at the beginning of a rainfall event affects the maximum increase of soil moisture, while a slight trend was visible comparing the initial soil moisture with the necessary rainfall amount to trigger a torrential flow.
    • Debris flow monitoring using load cells and pressure sensors on Sakura-jima Island

      Itoh, Takahiro; Fujimura, Naoki; Katou, Hitoshi; Tagata, Satoshi; Mizuyama, Takahisa (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Numerous debris flows have recently taken place frequently in Sakura-jima Island located at southwest in Japan due to rainfall events after ash deposition due to volcanic activities since 2010. Debris-flow measurement system with loadcell and pressure sensor (DFLP) had been applied for debris-flow monitoring (Osaka et al., 2014). In present study, a modified monitoring DELP system using load cells and a stainless-steel plate is employed. Mass density and sediment concentration are calculated using data obtained by the DFLP system and data measured by ultrasonic level meter and surface velocity by of image analyses of CCTV camera. (Results) Temporal changes of specific weight, sediment concentration and sediment volume of debris-flow in Nojiri and Arimura Rivers in 2014 were well measured using DFLP system. Sediment concentration and specific weight were calculated in both rivers, and there are at least 10 data in Arimura River and 8 data in Nojiri River for calculations of temporal changes of mass density and sediment concentration since 2012 and 2014, respectively. Averaged sediment concentration near peak discharge are calculated as 0.441 in Arimura River and 0.279 in Nojiri River, respectively. However, values of calculated concentration do not always take correlation with rainfall depth before debris-flow occurrences. Data analyses continuously need by more data collections of debris- flow events.
    • Implementation of an integrated management strategy to deal with landslide triggered debris flows: the Valloire case study (Savoie, France)

      Laigle, Dominique; Jongmans, Denis; Liebault, Frédéric; Baillet, Laurent; Rey, Etienne; Fontaine, Firmin; Borgniet, Laurent; Bonnefoy-Demongeot, Mylène; Ousset, Frédéric (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The Rieu Benoît is a debris-flow-prone catchment located in Valloire (Savoie, France). In 2011, a lateral landslide was detected about 600 m upstream of the fan apex where houses are present. This landslide has evolved slowly since 2011 but is likely, in case of rapid collapse, to provide up to 150,000 to 200,000 m3 of material to the channel and generate intense debris flows thus threatening human settlements on the fan and in the Valloire ski resort. This paper presents a contribution to the definition of a protection strategy based on the principle that a catastrophic evolution of the landslide can be detected sufficiently in advance to set up an effective alert procedure. Such early warning system can be designed provided (i) the landslide is instrumented to properly detect its evolution and characterize the volumes likely to mobilize into debris flows, this is carried out using photogrammetric, seismic, and electrical techniques; (ii) the interaction between the landslide and the channel is observed and sufficiently understood, this is carried out using a time-lapse camera taking a picture every two hours and at higher frequency once a flow is detected by a geophone; (iii) subsequent debris flows are observed and characterized in terms of flow thickness and velocity, this is carried out at a monitoring station located at the fan apex and equipped with a radar flow stage sensor and three geophones; (iv) consequences on urbanized areas are evaluated a priori on the basis of scenarios, this is carried out by simulating the spreading of debris flows for different volumes and material properties. The final step consists in building alert and evacuation procedures in collaboration with local authorities.